The present invention relates to a method of and an apparatus for releasing a cut-through connection.
Network services provided for data transmission can be classified into a connection type and a connection-less type.
In the connection-type network service, communication data is transmitted through a communication channel which has been established exclusively between a sender terminal and a receiver terminal according to a telephone number, for example, designated by the sender terminal.
On the other hand, communication data is transmitted being divided into packets, such as IP (Internet Protocol) packets, each added with a header having destination information, in the connection-less-type network service. The packet received by a node of the network is relayed to a next node retrieved by referring to routing information prepared in the node according to the destination information described in the header. Being thus relayed node by node, each packet finally arrives to a destination node which accommodates the receiver terminal of the packet.
In the connection-less-type network service, communication channels between the sender terminal and the receiver terminal can be shared by packets having various destinations, enabling a good use of the network resources.
However, in view of transmission speed, the connection-type network service is advantageous, and substantially the same efficiency of the network resources can be obtained even in the connection-type network service when there are many packets to be transmitted continuously from a specific sender terminal to a specific receiver terminal.
Recently, a network node device called the IP switch is developed, wherein an ATM (Asynchronous Transfer Mode) switch is employed together with an IP controller which takes charge of routing the IP packets by controlling the ATM switch.
In the IP switch, continuous flows of IP packets, such as a flow of multi-media data or burst data, are taken in consideration, and a VC (Virtual Channel) is assigned to each distinct continuous flow of the IP packets, so that ATM cells of the concerning flows can be relayed promptly by way of xe2x80x9ccell-switchingxe2x80x9d, that is, can be relayed directly by the ATM switch without reassembled into packet data.
In the IP switch, ATM cells of the IP packet arrived to the node for the first of each continuous flow are reassembled into packet data and transferred to the IP controller. When the IP packet is detected by the IP controller to belong to a continuous flow, such as a flow according to the FTP (File Transfer Protocol) or the HTTP (Hyper Text Transfer Protocol), a VC connection exclusively assigned to the flow is established in the ATM switch for performing a high-speed switching of the ATM cells of the flow, at the cell-level without passing the IP controller. This connection is called the cut-through connection.
The cut-through connection should be released when the concerning flow has been over, that is, when it is detected that any ATM cell of the concerning flow does not arrive for a predetermined time period.
Besides the IP switch, several network node devices, such as those called the LANE (LAN Emulation over ATM), the MPOA (Multi-Protocol Over ATM) or the IPOA (IP Over ATM), are proposed or developed in the ATM Forum or the IETF (Internet Engineering Task Force) by integrating the ATM and the IP technology.
In these network node devices, also, the cut-through connection is established for each continuous flow of the packet traffic, similarly to the IP switch, and established cut-through connections are monitored always individually for releasing them in the absence of their traffic for a certain time period.
For detecting the absence of the packet arrival for a certain period, a traffic monitoring means, which is realized conventionally with software and cell counters for counting cell arrivals on each cut-through connection, has been provided in any of the IP switch, the LANE, the MPOA and the IPOA.
FIG. 5 is a block diagram illustrating a configuration example of a conventional traffic monitoring means for detecting the absence of the cell arrival, and FIG. 6 is a flowchart illustrating operational steps performed in the software for controlling the monitoring means of FIG. 5.
A cell detecting unit 41 detects passage of ATM cells of each cut-through connection, which is notified to a cell counter 42 and the count value of the cell counter 42 is incremented by one with passage of one ATM cell.
In the software implemented in the IP controller, for example, initialization is performed (at step S20 of FIG. 6) when a cut-through connection is newly established. A register A for storing the preceding count value of the cell counter 42 and a soft counter, both provided in the software, are reset to xe2x80x980xe2x80x99, together with the cell counter 42, and a timing clock, which indicates a timing periodically to read out the cell counter 42, is started.
Every time the timing to read out the cell counter 42 arrives (YES at step S21), the count value of the cell counter 42 is read out (at step S22) and compared to the preceding count value of the cell counter 42 stored in the register A (at step S23).
When the count value is not equal to the preceding value, it means that at least one ATM cell of the cut-through connection is arrived and so, the concerning traffic is determined to be flowing normally. The preceding value stored in the register A is revised with the count value newly read out (at step S24), and the operational step returns to S21 for repeating steps S21 to S24.
When the count value of the cell counter 42 is detected to be equal to the preceding value (at step S23), the software counter is incremented by one (at step S25) as no ATM cell has arrived from the preceding read-out timing. Until the software counter counts a threshold value, the operational steps S21 to S26 are repeated. When the count value of the software counter attains to the threshold value, it is determined (at step S27) that the traffic of the corresponding cut-through connection has terminated, and the concerning cut-through connection is released.
However, a problem of the conventional traffic monitoring means as above described is that there must be performed many software processings, such as reading out the cell counter 42 (step S22), comparing the count value to the preceding value (steps S23 and S24), or revising the software counter (step S25). Therefore, when the number of established cut-through connections becomes large, load of the software to be executed in the IP controller, for example, becomes too much increased.
Another problem of the conventional traffic monitoring means is that a large memory space is required because the software counter and the register A should be provided for each cut-through connection.
Therefore, a primary object of the present invention is to provide a method of and an apparatus for releasing a cut-through connection which is applicable to such network node devices and able to reduce load to be charged on software processings.
In order to achieve the object, in an apparatus according to an aspect of the invention for releasing a cut-through connection in a network node when traffic on the cut-through connection becomes smaller than a fixed value by monitoring traffic of each of cut-through connections established in the network node, there are comprised:
a timer having a time counter assigned to the cut-through connection and outputting a time-out notification signal when a count value of the time counter has attained to a time-out threshold value determined corresponding to the cut-through connection, the time counter being incremented along with time passage and being reset when the cut-through connection is established and when a cell of the cut-through connection arrives to the network node;
a time-out threshold memory wherein the time-out threshold value is registered;
a connection-release control unit for controlling a cell processing unit to release the cut-through connection according to the time-out notification signal; and
a connection-release message generator for transmitting a connection-release requesting message of the cut-through connection towards a next node according to the time-out notification signal.
Therefore, the load to the control software for detecting traffic termination of the cut-through connections can be far reduced according to the invention in comparison with the conventional method.
An apparatus according to a second aspect of the invention comprises:
a timer having an up/down counter assigned to the cut-through connection and outputting a time-out notification signal when a count value of the up/down counter has attained to a time-out threshold value determined corresponding to the cut-through connection, the up/down counter being reset when the cut-through connection is established, being incremented according to clock pulses having a cell cycle predetermined for the cut-through connection and being decremented when a cell of the cut-through connection arrives to the network node;
a time-out threshold memory wherein the time-out threshold value is registered;
a cycle-clock generator for generating the clock pulses referring to a value of the cell cycle which is registered in a cell-cycle memory corresponding to the cut-through connection;
a connection-release control unit for controlling a cell processing unit to releasing the cut-through connection according to the time-out notification signal; and
a connection-release message generator for transmitting a connection-release requesting message of the cut-through connection towards a next node according to the time-out notification signal.
According to the second aspect, the time-out notification signal can be generated even when the average cell arrival cycle of a cut-through connection remains longer than a predetermined cell cycle for a certain time period. Therefore, also the cut-through connection whereof cell traffic has become too small can be released efficiently.